The experiment was carried out on rats. Unit discharges of NRM were recorded extracellularly with glass microelectrode. Before the lesion of the head of N. Caudatus, 15 NRM neurons were recorded. The stimulation of the hindlimb areas of SM could obviously activate NRM neurons, the spontaneous discharges were increased to 59.06 +/- 25.35% (P < 0.05) and the nociceptive responses were obviously inhibited to -46.61 +/- 14.78 (P < 0.01) at 0 minute after stopping stimulation. Both effects lasted for 15 minutes, and then gradually returned to original level. After the lesion of the head of N. Caudatus, the effects of the stimulation of the hindlimb areas of SM on 19 NRM neurons were clearly decreased. The spontaneous discharges were increased to only 6.9 +/- 21.46% and the nociceptive responses were inhibited only -4.57 +/- 11.08% at 0 minute after stopping stimulation, even the nociceptive responses were slightly increased in 5-30 minutes. The difference between the two groups was statistical significance. The value of the difference was about 42% (P < 0.05) at 0 minute and lasted 30 minutes. It suggests that the effects of stimulating SM on NRM may be transmitted by the head of N. Caudatus in the extrapyramidal system.